The Membrane

Typical membrane materials used for polymer electrolyte fuel cells are ionomers which are composed of perfluorinated polymer backbones with side-chains containing acid groups, most commonly sulfonic acid (–SO3H) end groups. In contact with water, the sulfonic acid groups dissociate and thus introduce protons as charge carriers into the membrane. At the same time, the remaining SO3– side-chain end groups become hydrated and form a neutralising partially ordered environment in which protons and water molecules move. Preferential interactions between water, protons and SO3– groups as a consequence of hydrogen bonding and ion solvation and between the hydrophobic polymer backbones lead to phase separation on the nanometer scale between polymer and aqueous phase. Protons move in the aqueous sub-phase, and hence the presence of water is essential for the material to become proton conducting.

The membrane in the polymer electrolyte fuel cell (PEFC) is a key component. Not by...